Rahm sunk a long-range putt as Europe quickly quashed what had looked like a comeback from Team USA after the visitors were mauled in the morning foursomes.
Following the match, Koepka said: “I want to hit a board and pout just like Jon Rahm did. But, you know, it is what is is. Act like a child. But we’re adults, we move on.”
Rahm carded two eagles in the final two holes to give him and playing partner Nicolai Hojgaard a half which felt like a win against Koepka and Scottie Scheffler.
European captain Luke Donald, after his side romped to a 6½-1½ lead at the end of day one, downplayed the apparent spat.
He said: “I certainly didn’t see any of that. Jon was a big support system for Nicolai today. Jon is a passionate person but I didn’t see him acting any other way.”
Responding to the comments, US skipper Zach Johnson added: “I’m sure Brooks is frustrated like all 12 of us, 18 of us are frustrated today and the result.”